Variable magnification optical system, optical apparatus, imaging apparatus and method for manufacturing variable magnification optical system

ABSTRACT

A variable magnification optical system includes a positive first lens group disposed at a most object side, a negative intermediate group disposed at an image side of the first lens group, a positive focusing group disposed at an image side of the intermediate group, and a positive image side group disposed at an image side of the focusing group. Upon varying magnification, a distance between the first lens group and the intermediate group, a distance between the intermediate group and the focusing group and a distance between the focusing group and the image side group are varied; and the image side group includes, in order from an object side, a positive A group, a negative B group satisfying a predetermined conditional expression with respect to the A group, and a C group, whereby excellent optical performance, high speed focusing, and other advantages are achieved.

TECHNICAL FIELD

The present invention relates to a variable magnification optical system, an optical apparatus, an imaging apparatus and a method for manufacturing the variable magnification optical system.

BACKGROUND ART

There has been proposed a variable magnification optical system that is suitable to be used for a photographic camera, an electronic still camera, a video camera and the like. For example, please refer to a Japanese Patent application Laid-Open Gazette No. H4-293007. However, a variable magnification optical system as disclosed in the Japanese Patent application Laid-Open Gazette No. H4-293007 is not intended to reduce a focusing group in weight sufficiently and is not suitable for attain high speed focusing operation.

PRIOR ART REFERENCE Patent Document

Patent Document 1: Japanese Patent application Laid-Open Gazette No. H4-293007.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provided a variable magnification optical system comprising a first lens group disposed at a most object side and having positive refractive power,

an intermediate group disposed at an image side of the first lens group and having negative refractive power,

a focusing group disposed at an image side of the intermediate group and having positive refractive power, the focusing group being moved upon focusing, and

an image side group disposed at an image side of the focusing group and having positive refractive power;

upon varying magnification, a distance between the first lens group and the intermediate group, a distance between the intermediate group and the focusing group and a distance between the focusing group and the image side group being varied; and

the image side group comprising, in order from an object side, an A group having positive refractive power, a B group satisfying the following conditional expression with respect to the A group and having negative refractive power, and a C group: 1.67<fA/(−fB)<2.80

where fA denotes a focal length of the A group,

and fB denotes a focal length of the B group.

Further, according to a second aspect of the present invention, there is provided a method for manufacturing a variable magnification optical system comprising steps of

arranging a first lens group disposed at a most object side and having positive refractive power, an intermediate group disposed at an image side of the first lens group and having negative refractive power, a focusing group disposed at an image side of the intermediate group and having positive refractive power, the focusing group being moved upon focusing, and an image side group disposed at an image side of the focusing group and having positive refractive power such that, upon varying magnification, a distance between the first lens group and the intermediate group, a distance between the intermediate group and the focusing group and a distance between the focusing group and the image side group are varied; and

arranging such that the image side group is composed of, in order from an object side, an A group having positive refractive power, a B group satisfying the following conditional expression with respect to the A group and having negative refractive power, and a C group: 1.67<fA/(−fB)<2.80

where fA denotes a focal length of the A group,

and fB denotes a focal length of the B group.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a variable magnification optical system according to a First Example.

FIGS. 2A, 2B and 2C are graphs showing various aberrations of the variable magnification optical system according to the First Example.

FIGS. 3A and 3B are graphs showing meridional transverse aberrations of the variable magnification optical system according to the First Example.

FIGS. 4A, 4B and 4C are graphs showing various aberrations of the variable magnification optical system according to the First Example.

FIG. 5 is a sectional view of a variable magnification optical system according to a Second Example.

FIGS. 6A, 6B and 6C are graphs showing various aberrations of the variable magnification optical system according to the Second Example.

FIGS. 7A and 7B are graphs showing meridional transverse aberrations of the variable magnification optical system according to the Second Example.

FIGS. 8A, 8B and 8C are graphs showing various aberrations of the variable magnification optical system according to the Second Example.

FIG. 9 is a sectional view of a variable magnification optical system according to a Third Example.

FIGS. 10A, 10B and 10C are graphs showing various aberrations of the variable magnification optical system according to the Third Example.

FIGS. 11A and 11B are graphs showing meridional transverse aberrations of the variable magnification optical system according to the Third Example.

FIGS. 12A, 12B and 12C are graphs showing various aberrations of the variable magnification optical system according to the Third Example.

FIG. 13 is a sectional view of a variable magnification optical system according to a Fourth Example.

FIGS. 14A, 14B and 14C are graphs showing various aberrations of the variable magnification optical system according to the Fourth Example.

FIGS. 15A and 15B are graphs showing meridional transverse aberrations of the variable magnification optical system according to the Fourth Example.

FIGS. 16A, 16B and 16C are graphs showing various aberrations of the variable magnification optical system according to the Fourth Example.

FIG. 17 is a sectional view of a variable magnification optical system according to a Fifth Example.

FIGS. 18A, 18B and 18C are graphs showing various aberrations of the variable magnification optical system according to the Fifth Example.

FIGS. 19A and 19B are graphs showing meridional transverse aberrations of the variable magnification optical system according to the Fifth Example.

FIGS. 20A, 20B and 20C are graphs showing various aberrations of the variable magnification optical system according to the Fifth Example.

FIG. 21 is a sectional view of a variable magnification optical system according to a Sixth Example.

FIGS. 22A, 22B and 22C are graphs showing various aberrations of the variable magnification optical system according to the Sixth Example.

FIGS. 23A and 23B are graphs showing meridional transverse aberrations of the variable magnification optical system according to the Sixth Example.

FIGS. 24A, 24B and 24C are graphs showing various aberrations of the variable magnification optical system according to the Sixth Example.

FIG. 25 is a sectional view of a variable magnification optical system according to a Seventh Example.

FIGS. 26A, 26B and 26C are graphs showing various aberrations of the variable magnification optical system according to the Seventh Example.

FIGS. 27A and 27B are graphs showing meridional transverse aberrations of the variable magnification optical system according to the Seventh Example.

FIGS. 28A, 28B and 28C are graphs showing various aberrations of the variable magnification optical system according to the Seventh Example.

FIG. 29 is a sectional view of a variable magnification optical system according to an Eighth Example.

FIGS. 30A, 30B and 30C are graphs showing various aberrations of the variable magnification optical system according to the Eighth Example.

FIGS. 31A and 31B are graphs showing meridional transverse aberrations of the variable magnification optical system according to the Eighth Example.

FIGS. 32A, 32B and 32C are graphs showing various aberrations of the variable magnification optical system according to the Eighth Example.

FIG. 33 shows a configuration of a camera equipped with the variable magnification optical system.

FIG. 34 is a flowchart schematically explaining a method for manufacturing the variable magnification optical system.

EMBODIMENT FOR CARRYING OUT THE INVENTION

Next, a variable magnification optical system according to the embodiment of the present invention, an optical apparatus, an imaging apparatus and a method for manufacturing the variable magnification optical system, will be explained.

The variable magnification optical system according to the present embodiment comprises a first lens group disposed at a most object side and having positive refractive power, an intermediate group disposed at an image side of the first lens group and having negative refractive power, a focusing group disposed at an image side of the intermediate group and having positive refractive power, the focusing group being moved upon focusing, and an image side group disposed at an image side of the focusing group and having positive refractive power; upon varying magnification, a distance between the first lens group and the intermediate group, a distance between the intermediate group and the focusing group and a distance between the focusing group and the image side group being varied; and the image side group being composed of, in order from an object side, an A group having positive refractive power, a B group satisfying the following conditional expression (1) with respect to the A group and having negative refractive power, and a C group: 1.67<fA/(−fB)<2.80  (1)

where fA denotes a focal length of the A group, and

fB denotes a focal length of the B group.

Further, in the variable magnification optical system according to the present embodiment, it is desirable that the focusing group is composed of one or two lens components.

Further, in the variable magnification optical system according to the present embodiment, it is desirable that the B group is disposed to be movable to have a displacement component in a direction perpendicular to the optical axis.

The focusing group of the present embodiment comprises at least one lens group. Further, the image side group of the present embodiment comprises at least one lens group. Furthermore, each of the A group, the B group and the C group of the present embodiment comprises at least one lens. Meanwhile, the term “lens group” in the present embodiment is a portion comprising at least one lens separated by an air space which varies upon varying magnification. Further, distance(s) between lenses included in lens groups in the present embodiment, is(are) not varied upon varying magnification, but is(are) changeable properly.

As described above, the variable magnification optical system according to the present embodiment comprises at least four lens groups and varies distances between lens groups upon varying magnification. With this configuration, it is possible to correct superbly various aberrations upon varying magnification.

Further, in the variable magnification optical system according to the present embodiment, as described above, the focusing group is composed of one or two lens components. With such configuration, the focusing group can be downsized and reduced in weight. Meanwhile, the term “lens component” in the present embodiment means a single lens or a cemented lens. Further, in the variable magnification optical system according to the present embodiment, the focusing group means a portion comprising at least one lens separated by an air space that changes upon focusing.

Furthermore, in the variable magnification optical system according to the present embodiment, as described above, the image side group is composed of, in order from the object side, the A group having positive refractive power, the B group having negative refractive power, and the C group, the B group being moved, as a vibration reduction group, to have a displacement component in a direction perpendicular to the optical axis. With such configuration, it is possible to correct displacement of imaging position caused by a camera shake or the like, in other words, vibration reduction can be carried out. Moreover, the vibration reduction group can be downsized, and in addition thereto deterioration in optical performance upon carrying out vibration reduction can be effectively suppressed. Meanwhile, the vibration reduction group in the present embodiment means a portion that is moved to have a component in a direction perpendicular to the optical axis upon carrying out vibration reduction.

The above conditional expression (1) defines a ratio of the focal length of the A group to the focal length of the B group that is the vibration reduction group. With satisfying the conditional expression (1), the variable magnification optical system according to the present embodiment can suppress effectively deterioration in optical performance upon carrying out vibration reduction.

When the value of fA/(−fB) is equal to or exceeds the upper limit value of the conditional expression (1) of the variable magnification optical system according to the present embodiment, refractive power of the vibration reduction group becomes large, and deterioration in eccentric coma aberration upon carrying out vibration reduction becomes large. Meanwhile, in order to ensure the advantageous effect of the present embodiment, it is preferable to set the upper limit value of the conditional expression (1) to 2.70. Further, in order to ensure the advantageous effect of the present embodiment more surely, it is preferable to set the upper limit value of the conditional expression (1) to 2.60.

On the other hand, when the value of fA/(−fB) is equal to or falls below the lower limit value of the conditional expression (1) of the variable magnification optical system according to the present embodiment, refractive power of the A group becomes large, and it becomes difficult to correct spherical aberration and other various aberrations. Further, refractive power of the vibration reduction group becomes small, and an amount of movement of the vibration reduction group upon carrying out vibration reduction becomes large. For this reason, a lens barrel that receives the variable magnification optical system according to the present embodiment becomes large in size, so this is not preferable. Meanwhile, in order to ensure the advantageous effect of the present embodiment, it is preferable to set the lower limit value of the conditional expression (1) to 1.68. Furthermore, in order to ensure the advantageous effect of the present embodiment more surely, it is preferable to set the lower limit value of the conditional expression (1) to 1.69.

With configurations as described above, it is possible to realize a variable magnification optical system having excellent optical performance and a focusing lens group reduced in weight in order to attain high speed focusing operation.

Further, in the variable magnification optical system according to the present embodiment, it is desirable that a distance between the A group and the B group is larger than a distance between the B group and the C group.

Further, in the variable magnification optical system according to the present embodiment, it is desirable that the following conditional expression (1A) is satisfied: 2.50<f1/(−fc)<6.20  (1A)

where f1 denotes a focal length of the first lens group, and fc denotes a focal length of the intermediate group.

The conditional expression (1A) defines a ratio of the focal length of the first lens group to the focal length of the intermediate group. With satisfying the conditional expression (1A), the variable magnification optical system according to the present embodiment can suppress variations in spherical aberration and other various aberrations upon varying magnification from a wide angle end state to a telephoto end state.

When the value of f1/(−fc) is equal to or exceeds the upper limit value of the conditional expression (1A) of the variable magnification optical system according to the present embodiment, refractive power of the intermediate group becomes large, and it becomes difficult to correct spherical aberration and other various aberrations. Meanwhile, in order to ensure the advantageous effect of the present embodiment, it is preferable to set the upper limit value of the conditional expression (1A) to 5.90. Further, in order to ensure the advantageous effect of the present embodiment more surely, it is preferable to set the upper limit value of the conditional expression (1A) to 5.60.

On the other hand, when the value of f1/(−fc) is equal to or falls below the lower limit value of the conditional expression (1A) of the variable magnification optical system according to the present embodiment, refractive power of the first lens group becomes large, and it becomes difficult to correct spherical aberration and other various aberrations. Meanwhile, in order to ensure the advantageous effect of the present embodiment, it is preferable to set the lower limit value of the conditional expression (1A) to 2.80. Furthermore, in order to ensure the advantageous effect of the present embodiment more surely, it is preferable to set the lower limit value of the conditional expression (1A) to 3.70.

Further, in the variable magnification optical system according to the present embodiment it is desirable that the following conditional expression (1B) is satisfied: 3.00<f1fw/ff<9.00  (1B)

where f1fw denotes a composite focal length from the first lens group to the focusing group in the wide angle end state, and ff denotes a focal length of the focusing group.

The conditional expression (1B) defines a ratio of the composite focal length from the first lens group to the focusing group in the wide angle end state to the focal length of the focusing group. With satisfying the conditional expression (1B), the variable magnification optical system according to the present embodiment can suppress variations in spherical aberration and other various aberrations upon focusing from an infinitely distant object to a close distance object in the wide angle end state.

When the value of f1fw/ff is equal to or exceeds the upper limit value of the conditional expression (1B) of the variable magnification optical system according to the present embodiment, refractive power of the focusing group becomes large, and it becomes difficult to suppress variations in spherical aberration and other various aberrations upon focusing from an infinitely distant object to a close distance object in the wide angle end state. Meanwhile, in order to ensure the advantageous effect of the present embodiment, it is preferable to set the upper limit value of the conditional expression (1B) to 8.50. Further, in order to ensure the advantageous effect of the present embodiment more surely, it is preferable to set the upper limit value of the conditional expression (1B) to 8.00.

On the other hand, when the value of f1fw/ff is equal to or falls below the lower limit value of the conditional expression (1B) of the variable magnification optical system according to the present embodiment, refractive power from the first lens group to the focusing group in the wide angle end state becomes large, and it becomes difficult to suppress variations in spherical aberration and other various aberrations upon focusing from an infinitely distant object to a close distance object in the wide angle end state. Meanwhile, in order to ensure the advantageous effect of the present embodiment, it is preferable to set the lower limit value of the conditional expression (1B) to 3.30. Furthermore, in order to ensure the advantageous effect of the present embodiment more surely, it is preferable to set the lower limit value of the conditional expression (1B) to 3.60.

Further, in the variable magnification optical system according to the present embodiment it is desirable that the following conditional expression (2) is satisfied: 1.50<f1/ff<2.35  (2)

where f1 denotes a focal length of the first lens group, and ff denotes a focal length of the focusing group.

The conditional expression (2) defines a ratio of the focal length of the first lens group to the focal length of the focusing group. With satisfying the conditional expression (2), the variable magnification optical system according to the present embodiment can suppress variations in spherical aberration and other various aberrations upon carrying out focusing from an infinitely distant object to a close distance object.

When the value of f1/ff is equal to or exceeds the upper limit value of the conditional expression (2) of the variable magnification optical system according to the present embodiment, refractive power of the focusing group becomes large, and it becomes difficult to suppress variations in spherical aberration and other various aberrations upon carrying out focusing from an infinitely distant object to a close distance object. Meanwhile, in order to ensure the advantageous effect of the present embodiment, it is preferable to set the upper limit value of the conditional expression (2) to 2.30. Further, in order to ensure the advantageous effect of the present embodiment more surely, it is preferable to set the upper limit value of the conditional expression (2) to 2.25.

On the other hand, when the value of f1/ff is equal to or falls below the lower limit value of the conditional expression (2) of the variable magnification optical system according to the present embodiment, refractive power of the first lens group becomes large, and it becomes difficult to correct spherical aberration and other various aberrations. Meanwhile, in order to ensure the advantageous effect of the present embodiment, it is preferable to set the lower limit value of the conditional expression (2) to 1.60. Furthermore, in order to ensure the advantageous effect of the present embodiment more surely, it is preferable to set the lower limit value of the conditional expression (2) to 1.70.

Further, in the variable magnification optical system according to the present embodiment it is desirable that the first lens group is moved toward the object side upon varying magnification from the wide angle end state to the telephoto end state. With such a configuration, the whole length of the variable magnification optical system according to the present embodiment can be reduced in the wide angle end state, thereby it becoming possible to downsize the variable magnification optical system according to the present embodiment.

Further, in the variable magnification optical system according to the present embodiment it is desirable that a distance between the focusing group and the image side group is increased upon varying magnification from the wide angle end state to the telephoto end state. With this configuration, various aberrations upon varying magnification can be corrected superbly. In particular, it is possible to secure sufficiently a space for moving the focusing group for focusing in the telephoto end state, so it is possible to correct excellently spherical aberration upon focusing on a close distance object in the telephoto end state.

Further, in the variable magnification optical system according to the present embodiment it is desirable that the following conditional expression (3) is satisfied: 0.25<ff/fi<1.10  (3)

where ff denotes a focal length of the focusing group, and fi denotes a focal length of the image side group.

The conditional expression (3) defines a ratio of the focal length of the focusing group to the focal length of the image side group. With satisfying the conditional expression (3), the variable magnification optical system according to the present embodiment can suppress variations in spherical aberration and other various aberrations upon focusing from an infinitely distant object to a close distance object.

When the value of ff/fi is equal to or exceeds the upper limit value of the conditional expression (3) of the variable magnification optical system according to the present embodiment, refractive power of the image side group becomes large, and it becomes difficult to suppress coma aberration and other various aberrations. Meanwhile, in order to ensure the advantageous effect of the present embodiment, it is preferable to set the upper limit value of the conditional expression (3) to 1.05. Further, in order to ensure the advantageous effect of the present embodiment more surely, it is preferable to set the upper limit value of the conditional expression (3) to 1.00.

On the other hand, when the value of ff/fi is equal to or falls below the lower limit value of the conditional expression (3) of the variable magnification optical system according to the present embodiment, refractive power of the focusing group becomes large, and it becomes difficult to correct variations in spherical aberration and other various aberrations upon focusing from an infinitely distant object to a close distance object. Meanwhile, in order to ensure the advantageous effect of the present embodiment, it is preferable to set the lower limit value of the conditional expression (3) to 0.28. Furthermore, in order to ensure the advantageous effect of the present embodiment more surely, it is preferable to set the lower limit value of the conditional expression (3) to 0.31.

Further, in the variable magnification optical system according to the present embodiment it is desirable that the following conditional expression (4) is satisfied: 1.80<fi/(−fB)<5.20  (4)

where fi denotes a focal length of the image side group, and fB denotes a focal length of the B group.

The conditional expression (4) defines a ratio of the focal length of the image side group to the focal length of the B group that is the vibration reduction group. With satisfying the conditional expression (4), the variable magnification optical system according to the present embodiment can suppress effectively deterioration of optical performance upon carrying out vibration reduction.

When the value of fi/(−fB) is equal to or exceeds the upper limit value of the conditional expression (4) of the variable magnification optical system according to the present embodiment, refractive power of the vibration reduction group becomes large, and deterioration of eccentric coma aberration upon carrying out vibration reduction becomes large. Meanwhile, in order to ensure the advantageous effect of the present embodiment, it is preferable to set the upper limit value of the conditional expression (4) to 5.00. Further, in order to ensure the advantageous effect of the present embodiment more surely, it is preferable to set the upper limit value of the conditional expression (4) to 4.90.

On the other hand, when the value of fi/(−fB) is equal to or falls below the lower limit value of the conditional expression (4) of the variable magnification optical system according to the present embodiment, refractive power of the image side group becomes large, and it becomes difficult to correct coma aberration and other various aberrations. Further, refractive power of the vibration reduction group becomes small, and an amount of movement of the vibration reduction group upon carrying out vibration reduction becomes large. For this reason, a lens barrel that receives the variable magnification optical system according to the present embodiment becomes large in size, so this is not preferable. Meanwhile, in order to ensure the advantageous effect of the present embodiment, it is preferable to set the lower limit value of the conditional expression (4) to 1.90. Further, in order to ensure the advantageous effect of the present embodiment more surely, it is preferable to set the lower limit value of the conditional expression (4) to 2.00.

Further, in the variable magnification optical system according to the present embodiment, it is desirable that the first lens group comprises at least two positive lenses. With this configuration, spherical aberration and chromatic aberration can be corrected effectively.

Further, in the variable magnification optical system according to the present embodiment, it is desirable that the focusing group is composed of one lens component. With this configuration, the focusing group can be made smaller in size and made lighter in weight.

Further, in the variable magnification optical system according to the present embodiment, it is desirable that the focusing group is composed of one single lens. With this configuration, the focusing group can be made lighter in weight.

Further, in the variable magnification optical system according to the present embodiment, it is desirable that the focusing group comprises at least one positive lens and the following conditional expression (5) is satisfied: 58.00<νFP  (5)

where νFP denotes an Abbe number for d-line (wavelength 587.6 nm) of the positive lens comprised in the focusing group.

The conditional expression (5) defines an Abbe number of the positive lens comprised in the focusing group. With satisfying the conditional expression (5), the variable magnification optical system according to the present embodiment can suppress variation in chromatic aberration upon focusing from an infinitely distant object to a close distance object.

When the value of νFP is equal to or falls below the lower limit value of the conditional expression (5) of the variable magnification optical system according to the present embodiment, large chromatic aberration in the focusing group occurs, so that variation in chromatic aberration upon focusing from an infinitely distant object to a close distance object becomes large. Meanwhile, in order to ensure the advantageous effect of the present embodiment, it is preferable to set the lower limit value of the conditional expression (5) to 59.00. Furthermore, in order to ensure the advantageous effect of the present embodiment more surely, it is preferable to set the lower limit value of the conditional expression (5) to 60.00.

Further, in the variable magnification optical system according to the present embodiment it is desirable that the following conditional expression (6) is satisfied: 0.15<ff/ft<0.30  (6)

where ff denotes a focal length of the focusing group, and ft denotes a focal length of the variable magnification optical system in the telephoto end state.

The conditional expression (6) defines a ratio of the focal length of the focusing group to the focal length of the variable magnification optical system according to the present embodiment in the telephoto end state. With satisfying the conditional expression (6), the variable magnification optical system according to the present embodiment can suppress variations in spherical aberration and other various aberrations upon focusing from an infinitely distant object to a close distance object.

When the value of ff/ft is equal to or exceeds the upper limit value of the conditional expression (6) of the variable magnification optical system according to the present embodiment, an amount of movement of the focusing group upon focusing from an infinitely distant object to a close distance object becomes large, and it becomes difficult to suppress variations in spherical aberration and other various aberrations. Meanwhile, in order to ensure the advantageous effect of the present embodiment, it is preferable to set the upper limit value of the conditional expression (6) to 0.28. Further, in order to ensure the advantageous effect of the present embodiment more surely, it is preferable to set the upper limit value of the conditional expression (6) to 0.26.

On the other hand, when the value of ff/ft is equal to or falls below the lower limit value of the conditional expression (6) of the variable magnification optical system according to the present embodiment, refractive power of the focusing group becomes large, and it becomes difficult to correct variations in spherical aberration and other various aberrations upon focusing from an infinitely distant object to a close distance object. Meanwhile, in order to ensure the advantageous effect of the present embodiment, it is preferable to set the lower limit value of the conditional expression (6) to 0.17. Furthermore, in order to ensure the advantageous effect of the present embodiment more surely, it is preferable to set the lower limit value of the conditional expression (6) to 0.19.

An optical apparatus according to an embodiment of the present invention comprises a variable magnification optical system configured as above-mentioned.

An imaging apparatus according to an embodiment of the present invention is equipped with a variable magnification optical system configured as above-mentioned and an imaging unit for capturing an image formed by the variable magnification optical system.

With such configurations, it is possible to realize an optical apparatus and an imaging apparatus which have excellent optical performance and a focusing lens group reduced in weight in order to attain high speed focusing operation.

According to an embodiment of the present invention, there is provided a method for manufacturing a variable magnification optical system comprising steps of arranging a first lens group disposed at a most object side and having positive refractive power, an intermediate group disposed at an image side of the first lens group and having negative refractive power, a focusing group disposed at an image side of the intermediate group and having positive refractive power, the focusing group being moved upon focusing, and an image side group disposed at an image side of the focusing group and having positive refractive power such that, upon varying magnification, a distance between the first lens group and the intermediate group, a distance between the intermediate group and the focusing group and a distance between the focusing group and the image side group are varied; and arranging such that the image side group is composed of, in order from an object side, an A group having positive refractive power, a B group satisfying the following conditional expression (1) with respect to the A group and having negative refractive power, and a C group: 1.67<fA/(−fB)<2.80  (1)

where fA denotes a focal length of the A group, and

fB denotes a focal length of the B group.

With such configurations, it is possible to manufacture a variable magnification optical system which has excellent optical performance and a focusing lens group reduced in weight in order to attain high speed focusing operation.

Hereinafter, examples relating to a variable magnification optical system according to an embodiment of the present invention will be explained with reference to the accompanying drawings.

First Example

FIG. 1 is a sectional view of a variable magnification optical system according to a First Example. Note that each arrow in FIG. 1 and FIGS. 5, 9, 13, 17, 21, 25 and 29 as described later indicates moving trajectory of each lens group upon varying magnification from the wide angle end state (W) to the telephoto end state (T).

The variable magnification optical system according to the First Example is composed of, in order from an object side, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, and a rear group GR having positive refractive power. The rear group GR is composed of, in order from the object side, a third lens group G3 having positive refractive power, and a fourth lens group G4 having positive refractive power.

The first lens group G1 consists of, in order from the object side, a double convex positive lens L11, and a cemented positive lens constructed by a negative meniscus lens L12 having a convex surface facing the object side cemented with a positive meniscus lens L13 having a convex surface facing the object side.

The second lens group G2 consists of, in order from the object side, a cemented negative lens constructed by a double concave negative lens L21 cemented with a positive meniscus lens L22 having a convex surface facing the object side, and a double concave negative lens L23.

The third lens group G3 consists of a double convex positive lens L31.

The fourth lens group G4 is composed of, in order from the object side, an A group G4A having positive refractive power, a B group G4B having negative refractive power, and a C group G4C having positive refractive power. Meanwhile, an aperture stop S is disposed between the A group G4A and the B group G4B.

The A group G4A consists of, in order from the object side, a cemented positive lens constructed by a double convex positive lens L41 cemented with a double concave negative lens L42, and a double convex positive lens L43.

The B group G4B consists of, in order from the object side, a cemented negative lens constructed by a double convex positive lens L44 cemented with a double concave negative lens L45.

The C group G4C consists of, in order from the object side, a double convex positive lens L46, and a negative meniscus lens L47 having a concave surface facing the object side.

In the variable magnification optical system according to the First Example, the first to fourth lens groups G1 to G4 are moved along the optical axis so that, upon varying magnification between the wide angle end state and the telephoto end state, a distance between the first lens group G1 and the second lens group G2, a distance between the second lens group G2 and the third lens group G3 and a distance between the third lens group G3 and the fourth lens group G4 are varied.

In the variable magnification optical system according to the First Example, the third lens group G3 is moved toward an image side along the optical axis, as the focusing lens group, thereby focusing from an infinitely distant object to a close distance object.

In the variable magnification optical system according to the First Example, the B group G4B is moved, as a vibration reduction group, to have a component in a direction perpendicular to the optical axis, thereby carrying out vibration reduction. Meanwhile, upon carrying out vibration reduction, positions of the A group G4A and the C group G4C in a direction perpendicular to the optical axis are fixed.

It is noted that in a lens having a focal length f of the whole lens system and a vibration reduction coefficient K (a ratio of a moving amount of an image on the image plane I to a moving amount of the vibration reduction group), it is possible to correct a rotational camera shake of an angle θ, by moving the vibration reduction group by the amount of (f·tan θ)/K perpendicularly to the optical axis. Accordingly, in the variable magnification optical system according to the First Example, in the wide angle end state, the vibration reduction coefficient is 1.06, and the focal length is 71.40 (mm), so that the moving amount of the B group G4B for correcting a rotational camera shake of 0.30 degrees is 0.35 (mm). In the telephoto end state, the vibration reduction coefficient is 1.86, and the focal length is 294.00 (mm), so that the moving amount of the B group G4B for correcting a rotational camera shake of 0.20 degrees is 0.55 (mm).

Table 1 below shows various values of the variable magnification optical system according to the First Example.

In table 1, “f” denotes a focal length, and “BF” denotes a back focal length (a distance on the optical axis between a most image side lens surface and the image plane I).

In [Surface Data], a surface number denotes an order of an optical surface counted from the object side, “r” denotes a radius of curvature, “d” denotes a surface-to-surface distance (a distance from an n-th surface to an (n+1)-th surface, where n is an integer), “nd” denotes refractive index for d-line (wavelength 587.6 nm) and “νd” denotes an Abbe number for d-line (wavelength 587.6 nm). Further, “Object Plane” denotes an object surface, “variable” denotes a variable surface-to-surface distance, “Stop S” denotes an aperture stop, and “I” denotes an image plane. Meanwhile, radius of curvature r=∞ denotes a plane surface. Refractive index of air nd=1.00000 is omitted.

In [Various Data], “FNO” denotes an F-number, “2ω” denotes an angle of view (unit “°”), “Ymax” denotes a maximum image height, “TL” denotes a total length of the variable magnification optical system according to the First Example (a distance along the optical axis from the first surface to the image plane I), and “dn” denotes a variable distance between an n-th surface and an (n+1)-th surface. Meanwhile, “W” denotes a wide angle end state, “M” denotes an intermediate focal length state, “T” denotes a telephoto end state, “Infinitely distant” denotes a time when focusing on an infinitely distant object is conducted, and “Close distance” denotes a time when focusing on a close distance object is conducted.

In [Lens Group Data], a starting surface and a focal length for each lens group are shown.

In [Values for Conditional Expressions], values corresponding to respective conditional expressions of the variable magnification optical system according to the First Example are shown.

Here, that “mm” is generally used for the unit of length such as the focal length f, the radius of curvature r and the unit for other lengths shown in Table 1. However, since similar optical performance can be obtained by an optical system proportionally enlarged or reduced in its dimension, the unit is not necessarily to be limited to “mm”.

The reference symbols in Table 1 described above, are used in the same way in Tables for the other Examples.

TABLE 1 First Example [Surface Data] Surface number r d nd νd Object Plane ∞  1 72.3688 6.972 1.51680 63.88  2 −604.5951 0.499  3 88.4675 1.500 1.62004 36.40  4 32.5526 8.844 1.51680 63.88  5 149.4554 variable  6 −453.8182 1.000 1.69680 55.52  7 18.7304 3.761 1.80518 25.45  8 40.0562 3.501  9 −33.7169 1.000 1.69680 55.52 10 3769.5898 variable 11 91.7620 4.268 1.51680 63.88 12 −46.5887 variable 13 54.6217 5.361 1.48749 70.31 14 −31.8367 1.000 1.85026 32.35 15 829.9126 0.200 16 34.8197 4.124 1.48749 70.31 17 −190.4880 1.633 18 (Stop S) ∞ 27.478  19 316.7035 2.575 1.80518 25.45 20 −37.0122 1.000 1.74400 44.81 21 28.1012 3.267 22 27.6380 3.921 1.54814 45.79 23 −54.2282 2.418 24 −22.4640 1.000 1.77250 49.62 25 −55.2971 BF Image Plane ∞ [Various Data] Variable magnification ratio 4.12 W M T f 71.4 105.0 294.0 FNO 4.17 4.18 6.38 2ω 22.84 15.30 5.48 Ymax 14.25 14.25 14.25 TL 166.32 183.64 219.32 BF 38.52 38.53 73.71 Infinitely distant d5 3.555 24.790 43.361 d10 26.610 21.614 2.000 d12 12.316 13.381 14.933 Close distance d5 3.555 24.790 43.361 d10 27.368 22.723 3.114 d12 11.558 12.271 13.819 [Lens Group Data] Group Starting Surface f 1 1 115.478 2 6 −26.653 3 11 60.427 4 13 138.481 [Values for Conditional Expression] (1) fA/(−fB) = 1.717 (1A) f1/(−fc) = 4.333 (1B) f1fw/ff = 6.400 (2) f1/ff = 1.911 (3) ff/fi = 0.436 (4) fi/(−fB) = 3.064 (5) νFP = 63.88 (6) ff/ft = 0.206

FIGS. 2A, 2B and 2C are graphs showing various aberrations of the variable magnification optical system according to the First Example upon focusing on an infinitely distant object, in which FIG. 2A is in a wide angle end state, FIG. 2B is in an intermediate focal length state, and FIG. 2C is in the telephoto end state.

FIG. 3A is a graph showing meridional transverse aberration of the variable magnification optical system according to the First Example upon focusing on an infinitely distant object in the wide angle end state with carrying out vibration reduction against a rotational camera shake of 0.30 degrees, and FIG. 3B is a graph showing meridional transverse aberration of the variable magnification optical system according to the First Example upon focusing on an infinitely distant object in the telephoto end state with carrying out vibration reduction against a rotational camera shake of 0.20 degrees.

FIGS. 4A, 4B and 4C are graphs showing various aberrations of the variable magnification optical system according to the First Example upon focusing on a close distance object, in which FIG. 4A is in the wide angle end state, FIG. 4B is in the intermediate focal length state, and FIG. 4C is in the telephoto end state.

In respective aberration graphs, FNO denotes an F-number, Y denotes an image height, and NA denotes a numerical aperture. For more information, there are shown a value of F-number FNO or numerical aperture NA corresponding to the maximum diameter in a spherical aberration graph, the maximum value of the image height Y in each of an astigmatism graph and a distortion graph, and a value of each image height in a coma aberration graph. Additionally, in respective aberration graphs, d denotes an aberration at d-line (wavelength 587.6 nm), and g denotes an aberration at g-line (wavelength 435.8 nm). In the astigmatism graph, a solid line indicates a sagittal image plane, and a broken line indicates a meridional image plane. The coma aberration graph shows a coma aberration for each image height Y. Incidentally, the same symbols as used in the First Example are employed in the other Examples as described later.

As is apparent from the respective aberration graphs, the variable magnification optical system according to the First Example shows superb imaging performance as a result of good corrections to various aberrations in the wide angle end state to the telephoto end state, and also shows superb imaging performance upon carrying out vibration reduction and upon focusing on a close distance object.

Second Example

FIG. 5 is a sectional view of a variable magnification optical system according to a Second Example.

The variable magnification optical system according to the Second Example is composed of, in order from an object side, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, and a rear group GR having positive refractive power. The rear group GR is composed of, in order from the object side, a third lens group G3 having positive refractive power, and a fourth lens group G4 having positive refractive power.

The first lens group G1 consists of, in order from the object side, a double convex positive lens L11, and a cemented positive lens constructed by a negative meniscus lens L12 having a convex surface facing the object side cemented with a positive meniscus lens L13 having a convex surface facing the object side.

The second lens group G2 consists of, in order from the object side, a cemented negative lens constructed by a double concave negative lens L21 cemented with a positive meniscus lens L22 having a convex surface facing the object side, and a double concave negative lens L23.

The third lens group G3 consists of a double convex positive lens L31.

The fourth lens group G4 is composed of, in order from the object side, an A group G4A having positive refractive power, a B group G4B having negative refractive power, and a C group G4C having positive refractive power. Meanwhile, an aperture stop S is disposed between the A group G4A and the B group G4B.

The A group G4A consists of, in order from the object side, a cemented positive lens constructed by a double convex positive lens L41 cemented with a negative meniscus lens L42 having a concave surface facing the object side.

The B group G4B consists of, in order from the object side, a cemented negative lens constructed by a positive meniscus lens L43 having a concave surface facing the object side cemented with a double concave negative lens L44.

The C group G4C consists of, in order from the object side, a double convex positive lens L45 and a negative meniscus lens L46 having a concave surface facing the object side.

In the variable magnification optical system according to the Second Example, the first to fourth lens groups G1 to G4 are moved along the optical axis so that, upon varying magnification between the wide angle end state and the telephoto end state, a distance between the first lens group G1 and the second lens group G2, a distance between the second lens group G2 and the third lens group G3 and a distance between the third lens group G3 and the fourth lens group G4 are varied.

In the variable magnification optical system according to the Second Example, the third lens group G3 is moved toward an image side along the optical axis, as the focusing lens group, thereby focusing from an infinitely distant object to a close distance object.

In the variable magnification optical system according to the Second Example, the B group G4B is moved, as a vibration reduction group, to have a component in a direction perpendicular to the optical axis, thereby conducting vibration reduction. Meanwhile, upon carrying out vibration reduction, positions of the A group G4A and the C group G4C in a direction perpendicular to the optical axis are fixed.

It is noted that in the variable magnification optical system according to the Second Example, in the wide angle end state, the vibration reduction coefficient is 1.17, and the focal length is 71.35 (mm), so that the moving amount of the B group G4B for correcting a rotational camera shake of 0.30 degrees is 0.32 (mm). In the telephoto end state, the vibration reduction coefficient is 1.80, and the focal length is 294.00 (mm), so that the moving amount of the B group G4B for correcting a rotational camera shake of 0.20 degrees is 0.57 (mm).

Table 2 below shows various values of the variable magnification optical system according to the Second Example.

TABLE 2 Second Example [Surface Data] Surface number r d nd νd Object Plane ∞  1 84.0136 6.369 1.51680 63.88  2 −569.5201 0.287  3 111.7962 1.500 1.62004 36.40  4 36.8295 8.708 1.51680 63.88  5 239.6437 variable  6 −196.3998 1.000 1.69680 55.52  7 17.8250 4.472 1.80518 25.45  8 63.8758 2.220  9 −50.1550 1.000 1.80100 34.92 10 107.3132 variable 11 98.4276 3.799 1.51680 63.88 12 −44.7987 variable 13 33.5689 5.221 1.48749 70.31 14 −34.6171 1.000 1.75520 27.57 15 −464.1612 1.880 16 (Stop S) ∞ 31.253  17 −215.7008 3.558 1.80610 40.97 18 −18.9067 1.000 1.69680 55.52 19 29.6933 2.000 20 25.4517 4.902 1.51742 52.20 21 −34.1288 6.212 22 −19.1689 1.000 1.77250 49.62 23 −46.3649 BF Image Plane ∞ [Various Data] Variable magnification ratio 4.12 W M T f 71.4 105.0 294.0 FNO 4.70 4.74 6.44 2ω 22.84 15.30 5.46 Ymax 14.25 14.25 14.25 TL 167.32 188.67 222.32 BF 38.52 39.12 64.52 Infinitely distant d5 3.000 27.419 53.254 d10 29.124 23.882 2.000 d12 9.294 10.871 15.165 Close distance d5 3.000 27.419 53.254 d10 29.965 25.078 3.487 d12 8.453 9.675 13.679 [Lens Group Data] Group Starting Surface f 1 1 128.484 2 6 −29.436 3 11 60.115 4 13 180.542 [Values for Conditional Expression] (1) fA/(−fB) = 2.468 (1A) f1/(−fc) = 4.365 (1B) f1fw/ff = 3.954 (2) f1/ff = 2.137 (3) ff/fi = 0.333 (4) fi/(−fB) = 3.886 (5) νFP = 63.88 (6) ff/ft = 0.204

FIGS. 6A, 6B and 6C are graphs showing various aberrations of the variable magnification optical system according to the Second Example upon focusing on an infinitely distant object, in which FIG. 6A is in a wide angle end state, FIG. 6B is in an intermediate focal length state, and FIG. 6C is in a telephoto end state.

FIG. 7A is a graph showing meridional transverse aberration of the variable magnification optical system according to the Second Example upon focusing on an infinitely distant object in the wide angle end state with carrying out vibration reduction against a rotational camera shake of 0.30 degrees, and FIG. 7B is a graph showing meridional transverse aberration of the variable magnification optical system according to the Second Example upon focusing on an infinitely distant object in the telephoto end state with carrying out vibration reduction against a rotational camera shake of 0.20 degrees.

FIGS. 8A, 8B and 8C are graphs showing various aberrations of the variable magnification optical system according to the Second Example upon focusing on a close distance object, in which FIG. 8A is in the wide angle end state, FIG. 8B is in the intermediate focal length state, and FIG. 8C is in the telephoto end state.

As is apparent from the respective aberration graphs, the variable magnification optical system according to the Second Example shows superb imaging performance as a result of good corrections to various aberrations in the wide angle end state to the telephoto end state, and also shows superb imaging performance upon carrying out vibration reduction and upon focusing on a close distance object.

Third Example

FIG. 9 is a sectional view of a variable magnification optical system according to a Third Example.

The variable magnification optical system according to the Third Example is composed of, in order from an object side, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, and a rear group GR having positive refractive power. The rear group GR is composed of, in order from the object side, a third lens group G3 having positive refractive power, and a fourth lens group G4 having positive refractive power.

The first lens group G1 consists of, in order from the object side, a double convex positive lens L11, and a cemented positive lens constructed by a negative meniscus lens L12 having a convex surface facing the object side cemented with a positive meniscus lens L13 having a convex surface facing the object side.

The second lens group G2 consists of, in order from the object side, a cemented negative lens constructed by a double concave negative lens L21 cemented with a positive meniscus lens L22 having a convex surface facing the object side, and a double concave negative lens L23.

The third lens group G3 consists of a double convex positive lens L31.

The fourth lens group G4 is composed of, in order from the object side, an A group G4A having positive refractive power, a B group G4B having negative refractive power, and a C group G4C having positive refractive power. Meanwhile, an aperture stop S is disposed between the A group G4A and the B group G4B.

The A group G4A consists of, in order from the object side, a cemented positive lens constructed by a double convex positive lens L41 cemented with a negative meniscus lens L42 having a concave surface facing the object side.

The B group G4B consists of, in order from the object side, a cemented negative lens constructed by a positive meniscus lens L43 having a concave surface facing the object side cemented with a double concave negative lens L44.

The C group G4C consists of, in order from the object side, a double convex positive lens L45, and a cemented negative lens constructed by a double concave negative lens L46 cemented with a double convex positive lens L47.

In the variable magnification optical system according to the Third Example, the first to fourth lens groups G1 to G4 are moved along the optical axis so that, upon varying magnification between the wide angle end state and the telephoto end state, a distance between the first lens group G1 and the second lens group G2, a distance between the second lens group G2 and the third lens group G3 and a distance between the third lens group G3 and the fourth lens group G4 are varied.

In the variable magnification optical system according to the Third Example, the third lens group G3 is moved toward an image side along the optical axis, as the focusing lens group, thereby focusing from an infinitely distant object to a close distance object.

In the variable magnification optical system according to the Third Example, the B group G4B is moved, as a vibration reduction group, to have a component in a direction perpendicular to the optical axis, thereby conducting vibration reduction. Meanwhile, upon carrying out vibration reduction, positions of the A group G4A and the C group G4C in a direction perpendicular to the optical axis are fixed.

It is noted that in the variable magnification optical system according to the Third Example, in the wide angle end state, the vibration reduction coefficient is 1.22, and the focal length is 71.40 (mm), so that the moving amount of the B group G4B for correcting a rotational camera shake of 0.30 degrees is 0.31 (mm). In the telephoto end state, the vibration reduction coefficient is 1.79, and the focal length is 294.00 (mm), so that the moving amount of the B group G4B for correcting a rotational camera shake of 0.20 degrees is 0.57 (mm).

Table 3 below shows various values of the variable magnification optical system according to the Third Example.

TABLE 3 Third Example [Surface Data] Surface number r d nd νd Object Plane ∞  1 85.0462 5.776 1.51680 63.88  2 −660.6172 0.468  3 127.3802 1.500 1.62004 36.40  4 39.1726 7.903 1.51680 63.88  5 338.5447 variable  6 −132.1891 1.000 1.69680 55.52  7 19.2602 4.667 1.80518 25.45  8 76.0183 2.071  9 −54.4201 1.000 1.80100 34.92 10 119.2030 variable 11 101.6158 3.707 1.51680 63.88 12 −48.1136 variable 13 32.8274 5.339 1.48749 70.31 14 −36.1413 1.000 1.80518 25.45 15 −208.8127 1.719 16 (Stop S) ∞ 20.897  17 −111.8106 3.901 1.66755 41.87 18 −18.5066 1.000 1.58913 61.22 19 35.2076 2.000 20 26.2172 5.000 1.48749 70.31 21 −44.8232 10.387  22 −18.5590 1.000 1.77250 49.62 23 39.9065 4.006 1.60342 38.03 24 −29.6411 BF Image Plane ∞ [Various Data] Variable magnification ratio 4.12 W M T f 71.4 105.0 294.0 FNO 4.68 4.76 6.45 2ω 22.80 15.28 5.44 Ymax 14.25 14.25 14.25 TL 166.39 188.89 221.32 BF 38.52 39.12 64.52 Infinitely distant d5 3.000 27.909 54.414 d10 30.861 25.246 2.000 d12 9.676 12.274 16.047 Close distance d5 3.000 27.909 54.414 d10 31.772 26.533 3.581 d12 8.765 10.987 14.466 [Lens Group Data] Group Starting Surface f 1 1 130.814 2 6 −30.984 3 11 63.720 4 13 184.004 [Values for Conditional Expression] (1) fA/(−fB) = 1.836 (1A) f1/(−fc) = 4.222 (1B) f1fw/ff = 3.924 (2) f1/ff = 2.063 (3) ff/fi = 0.345 (4) fi/(−fB) = 3.433 (5) νFP = 63.88 (6) ff/ft = 0.216

FIGS. 10A, 10B and 10C are graphs showing various aberrations of the variable magnification optical system according to the Third Example upon focusing on an infinitely distant object, in which FIG. 10A is in a wide angle end state, FIG. 10B is in an intermediate focal length state, and FIG. 10C is in a telephoto end state.

FIG. 11A is a graph showing meridional transverse aberration of the variable magnification optical system according to the Third Example upon focusing on an infinitely distant object in the wide angle end state with carrying out vibration reduction against a rotational camera shake of 0.30 degrees, and FIG. 11B is a graph showing meridional transverse aberration of the variable magnification optical system according to the Third Example upon focusing on an infinitely distant object in the telephoto end state with carrying out vibration reduction against a rotational camera shake of 0.20 degrees.

FIGS. 12A, 12B and 12C are graphs showing various aberrations of the variable magnification optical system according to the Third Example upon focusing on a close distance object, in which FIG. 12A is in the wide angle end state, FIG. 12B is in the intermediate focal length state, and FIG. 12C is in the telephoto end state.

As is apparent from the respective aberration graphs, the variable magnification optical system according to the Third Example shows superb imaging performance as a result of good corrections to various aberrations in the wide angle end state to the telephoto end state, and also shows superb imaging performance upon carrying out vibration reduction and upon focusing on a close distance object.

Fourth Example

FIG. 13 is a sectional view of a variable magnification optical system according to a Fourth Example.

The variable magnification optical system according to the Fourth Example is composed of, in order from an object side, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, and a rear group GR having positive refractive power. The rear group GR is composed of, in order from the object side, a third lens group G3 having positive refractive power and a fourth lens group G4 having positive refractive power.

The first lens group G1 consists of, in order from the object side, a double convex positive lens L11, and a cemented positive lens constructed by a negative meniscus lens L12 having a convex surface facing the object side cemented with a positive meniscus lens L13 having a convex surface facing the object side.

The second lens group G2 consists of, in order from the object side, a cemented negative lens constructed by a double concave negative lens L21 cemented with a positive meniscus lens L22 having a convex surface facing the object side, and a double concave negative lens L23.

The third lens group G3 consists of a double convex positive lens L31.

The fourth lens group G4 is composed of, in order from the object side, an A group G4A having positive refractive power, a B group G4B having negative refractive power, and a C group G4C having positive refractive power. Meanwhile, an aperture stop S is disposed between the A group G4A and the B group G4B.

The A group G4A consists of, in order from the object side, a cemented positive lens constructed by a double convex positive lens L41 cemented with a negative meniscus lens L42 having a concave surface facing the object side.

The B group G4B consists of, in order from the object side, a cemented negative lens constructed by a positive meniscus lens L43 having a concave surface facing the object side cemented with a double concave negative lens L44.

The C group G4C consists of, in order from the object side, a double convex positive lens L45, and a cemented negative lens constructed by a double concave negative lens L46 cemented with a double convex positive lens L47.

In the variable magnification optical system according to the Fourth Example, the first to fourth lens groups G1 to G4 are moved along the optical axis so that, upon varying magnification between the wide angle end state and the telephoto end state, a distance between the first lens group G1 and the second lens group G2, a distance between the second lens group G2 and the third lens group G3 and a distance between the third lens group G3 and the fourth lens group G4 are varied.

In the variable magnification optical system according to the Fourth Example, the third lens group G3 is moved toward an image side along the optical axis, as the focusing lens group, thereby focusing from an infinitely distant object to a close distance object.

In the variable magnification optical system according to the Fourth Example, the B group G4B is moved, as a vibration reduction group, to have a component in a direction perpendicular to the optical axis, thereby conducting vibration reduction. Meanwhile, upon carrying out vibration reduction, positions of the A group G4A and the C group G4C in a direction perpendicular to the optical axis are fixed.

It is noted that in the variable magnification optical system according to the Fourth Example, in the wide angle end state, the vibration reduction coefficient is 1.21, and the focal length is 71.40 (mm), so that the moving amount of the B group G4B for correcting a rotational camera shake of 0.30 degrees is 0.31 (mm). In the telephoto end state, the vibration reduction coefficient is 1.79, and the focal length is 292.00 (mm), so that the moving amount of the B group G4B for correcting a rotational camera shake of 0.20 degrees is 0.57 (mm).

Table 4 below shows various values of the variable magnification optical system according to the Fourth Example.

TABLE 4 Fourth Example [Surface Data] Surface number r d nd νd Object Plane ∞  1 86.4475 5.443 1.51680 63.88  2 −981.1690 0.200  3 146.3378 1.500 1.62004 36.40  4 41.2453 8.000 1.51680 63.88  5 1154.1773 variable  6 −105.1301 1.000 1.69680 55.52  7 20.4832 4.124 1.80518 25.45  8 77.3629 1.964  9 −62.6354 1.000 1.83400 37.18 10 142.2611 variable 11 123.7504 3.431 1.58913 61.22 12 −57.1062 variable 13 33.8130 5.634 1.49700 81.73 14 −38.7693 1.000 1.80518 25.45 15 −194.5892 1.688 16 (Stop S) ∞ 21.000  17 −99.8095 3.775 1.66755 41.87 18 −18.8632 1.000 1.58913 61.22 19 36.8056 2.500 20 34.3226 3.724 1.51680 63.88 21 −51.2601 11.445  22 −20.6818 1.000 1.77250 49.62 23 51.2093 3.854 1.60342 38.03 24 −30.0976 BF Image Plane ∞ [Various Data] Variable magnification ratio 4.09 W M T f 71.4 100.0 292.0 FNO 4.70 4.69 6.48 2ω 22.78 16.04 5.48 Ymax 14.25 14.25 14.25 TL 169.32 189.52 221.32 BF 39.12 38.52 66.12 Infinitely distant d5 3.000 26.086 53.441 d10 32.425 27.561 2.000 d12 11.493 14.070 16.477 Close distance d5 3.000 26.086 53.441 d10 33.360 28.885 3.621 d12 10.558 12.746 14.856 [Lens Group Data] Group Starting Surface f 1 1 128.221 2 6 −31.614 3 11 66.796 4 13 176.525 [Values for Conditional Expression] (1) fA/(−fB) = 1.691 (1A) f1/(−fc) = 4.056 (1B) f1fw/ff = 4.017 (2) f1/ff = 1.920 (3) ff/fi = 0.378 (4) fi/(−fB) = 3.308 (5) νFP = 61.22 (6) ff/ft = 0.229

FIGS. 14A, 14B and 14C are graphs showing various aberrations of the variable magnification optical system according to the Fourth Example upon focusing on an infinitely distant object, in which FIG. 14A is in a wide angle end state, FIG. 14B is in an intermediate focal length state, and FIG. 14C is in a telephoto end state.

FIG. 15A is a graph showing meridional transverse aberration of the variable magnification optical system according to the Fourth Example upon focusing on an infinitely distant object in the wide angle end state with carrying out vibration reduction against a rotational camera shake of 0.30 degrees, and FIG. 15B is a graph showing meridional transverse aberration of the variable magnification optical system according to the Fourth Example upon focusing on an infinitely distant object in the telephoto end state with carrying out vibration reduction against a rotational camera shake of 0.20 degrees.

FIGS. 16A, 16B and 16C are graphs showing various aberrations of the variable magnification optical system according to the Fourth Example upon focusing on a close distance object, in which FIG. 16A is in the wide angle end state, FIG. 16B is in the intermediate focal length state, and FIG. 16C is in the telephoto end state.

As is apparent from the respective aberration graphs, the variable magnification optical system according to the Fourth Example shows superb imaging performance as a result of good corrections to various aberrations in the wide angle end state to the telephoto end state, and also shows superb imaging performance upon carrying out vibration reduction and upon focusing on a close distance object.

Fifth Example

FIG. 17 is a sectional view of a variable magnification optical system according to a Fifth Example.

The variable magnification optical system according to the Fifth Example is composed of, in order from an object side, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, and a rear group GR having positive refractive power. The rear group GR is composed of, in order from the object side, a third lens group G3 having positive refractive power, and a fourth lens group G4 having positive refractive power.

The first lens group G1 consists of, in order from the object side, a double convex positive lens L11, and a cemented positive lens constructed by a negative meniscus lens L12 having a convex surface facing the object side cemented with a positive meniscus lens L13 having a convex surface facing the object side.

The second lens group G2 consists of, in order from the object side, a cemented negative lens constructed by a double concave negative lens L21 cemented with a positive meniscus lens L22 having a convex surface facing the object side, and a double concave negative lens L23.

The third lens group G3 consists of a double convex positive lens L31.

The fourth lens group G4 is composed of, in order from the object side, an A group G4A having positive refractive power, a B group G4B having negative refractive power, and a C group G4C having positive refractive power. Meanwhile, an aperture stop S is disposed between the A group G4A and the B group G4B.

The A group G4A consists of, in order from the object side, a cemented positive lens constructed by a double convex positive lens L41 cemented with a negative meniscus lens L42 having a concave surface facing the object side.

The B group G4B consists of, in order from the object side, a cemented negative lens constructed by a positive meniscus lens L43 having a concave surface facing the object side cemented with a double concave negative lens L44.

The C group G4C consists of, in order from the object side, a cemented positive lens constructed by a double convex positive lens L45 cemented with a negative meniscus lens L46 having a concave surface facing the object side, and a negative meniscus lens L47 having a concave surface facing the object side.

In the variable magnification optical system according to the Fifth Example, the first to fourth lens groups G1 to G4 are moved along the optical axis so that, upon varying magnification between the wide angle end state and the telephoto end state, a distance between the first lens group G1 and the second lens group G2, a distance between the second lens group G2 and the third lens group G3 and a distance between the third lens group G3 and the fourth lens group G4 are varied.

In the variable magnification optical system according to the Fifth Example, the third lens group G3 is moved toward an image side along the optical axis, as the focusing lens group, thereby focusing from an infinitely distant object to a close distance object.

In the variable magnification optical system according to the Fifth Example, the B group G4B is moved, as a vibration reduction group, to have a component in a direction perpendicular to the optical axis, thereby conducting vibration reduction. Meanwhile, upon carrying out vibration reduction, positions of the A group G4A and the C group G4C in a direction perpendicular to the optical axis are fixed.

It is noted that in the variable magnification optical system according to the Fifth Example, in the wide angle end state, the vibration reduction coefficient is 1.61, and the focal length is 72.10 (mm), so that the moving amount of the B group G4B for correcting a rotational camera shake of 0.30 degrees is 0.23 (mm). In the telephoto end state, the vibration reduction coefficient is 2.44, and the focal length is 292.00 (mm), so that the moving amount of the B group G4B for correcting a rotational camera shake of 0.20 degrees is 0.42 (mm).

Table 5 below shows various values of the variable magnification optical system according to the Fifth Example.

TABLE 5 Fifth Example [Surface Data] Surface number r d nd νd Object Plane ∞  1 90.0000 5.600 1.51680 63.88  2 −517.3850 0.200  3 123.0815 1.700 1.62004 36.40  4 39.0000 7.800 1.51680 63.88  5 324.1762 variable  6 −110.0000 1.300 1.69680 55.52  7 21.2201 3.957 1.84666 23.80  8 73.0429 1.848  9 −75.3714 1.200 1.85026 32.35 10 106.1768 variable 11 148.9696 3.374 1.58913 61.22 12 −56.4978 variable 13 28.2564 5.746 1.49700 81.73 14 −48.4258 1.200 1.84666 23.80 15 −580.3411 2.897 16 (Stop S) ∞ 23.051  17 −77.0000 3.951 1.72825 28.38 18 −14.4874 1.000 1.67003 47.14 19 29.3362 2.500 20 29.8903 5.510 1.62004 36.40 21 −17.4201 1.000 1.84666 23.80 22 −35.2773 7.314 23 −22.7541 1.000 1.77250 49.62 24 −46.2730 BF Image Plane ∞ [Various Data] variable magnification ratio 4.05 W M T f 72.1 100.0 292.0 FNO 4.70 4.63 6.53 2ω 22.62 16.08 5.50 Ymax 14.25 14.25 14.25 TL 169.32 187.97 221.32 BF 39.61 38.52 66.61 Infinitely distant d5 3.001 26.619 53.461 d10 33.373 28.524 2.000 d12 11.187 12.162 17.100 Close distance d5 3.001 26.619 53.461 d10 34.372 29.969 3.698 d12 10.188 10.718 15.402 [Lens Group Data] Group Starting Surface f 1 1 131.155 2 6 −32.550 3 11 69.956 4 13 165.331 [Values for Conditional Expression] (1) fA/(−fB) = 2.356 (1A) f1/(−fc) = 4.029 (1B) f1fw/ff = 4.519 (2) f1/ff = 1.902 (3) ff/fi = 0.417 (4) fi/(−fB) = 4.755 (5) νFP = 61.22 (6) ff/ft = 0.236

FIGS. 18A, 18B and 18C are graphs showing various aberrations of the variable magnification optical system according to the Fifth Example upon focusing on an infinitely distant object, in which FIG. 18A is in a wide angle end state, FIG. 18B is in an intermediate focal length state, and FIG. 18C is in a telephoto end state.

FIG. 19A is a graph showing meridional transverse aberration of the variable magnification optical system according to the Fifth Example upon focusing on an infinitely distant object in the wide angle end state with carrying out vibration reduction against a rotational camera shake of 0.30 degrees, and FIG. 19B is a graph showing meridional transverse aberration of the variable magnification optical system according to the Fifth Example upon focusing on an infinitely distant object in the telephoto end state with carrying out vibration reduction against a rotational camera shake of 0.20 degrees.

FIGS. 20A, 20B and 20C are graphs showing various aberrations of the variable magnification optical system according to the Fifth Example upon focusing on a close distance object, in which FIG. 20A is in the wide angle end state, FIG. 20B is in the intermediate focal length state, and FIG. 20C is in the telephoto end state.

As is apparent from the respective aberration graphs, the variable magnification optical system according to the Fifth Example shows superb imaging performance as a result of good corrections to various aberrations in the wide angle end state to the telephoto end state, and also shows superb imaging performance upon carrying out vibration reduction and upon focusing on a close distance object.

Sixth Example

FIG. 21 is a sectional view of a variable magnification optical system according to a Sixth Example.

The variable magnification optical system according to the Sixth Example is composed of, in order from an object side, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, and a rear group GR having positive refractive power. The rear group GR is composed of, in order from the object side, a third lens group G3 having positive refractive power, and a fourth lens group G4 having positive refractive power.

The first lens group G1 consists of, in order from the object side, a double convex positive lens L11, and a cemented positive lens constructed by a negative meniscus lens L12 having a convex surface facing the object side cemented with a positive meniscus lens L13 having a convex surface facing the object side.

The second lens group G2 consists of, in order from the object side, a cemented negative lens constructed by a double concave negative lens L21 cemented with a positive meniscus lens L22 having a convex surface facing the object side, and a double concave negative lens L23.

The third lens group G3 consists of a double convex positive lens L31.

The fourth lens group G4 is composed of, in order from the object side, an A group G4A having positive refractive power, a B group G4B having negative refractive power, and a C group G4C having positive refractive power. Meanwhile, an aperture stop S is disposed between the A group G4A and the B group G4B.

The A group G4A consists of, in order from the object side, a cemented positive lens constructed by a double convex positive lens L41 cemented with a double concave negative lens L42, and a double convex positive lens L43.

The B group G4B consists of, in order from the object side, a cemented negative lens constructed by a negative meniscus lens L44 having a concave surface facing the object side cemented with a double concave negative lens L45.

The C group G4C consists of, in order from the object side, a double convex positive lens L46, and a negative meniscus lens L47 having a concave surface facing the object side.

In the variable magnification optical system according to the Sixth Example, the first to fourth lens groups G1 to G4 are moved along the optical axis so that, upon varying magnification between the wide angle end state and the telephoto end state, a distance between the first lens group G1 and the second lens group G2, a distance between the second lens group G2 and the third lens group G3 and a distance between the third lens group G3 and the fourth lens group G4 are varied.

In the variable magnification optical system according to the Sixth Example, the third lens group G3 is moved toward an image side along the optical axis, as the focusing lens group, thereby focusing from an infinitely distant object to a close distance object.

In the variable magnification optical system according to the Sixth Example, the B group G4B is moved, as a vibration reduction group, to have a component in a direction perpendicular to the optical axis, thereby conducting vibration reduction. Meanwhile, upon carrying out vibration reduction, positions of the A group G4A and the C group G4C in a direction perpendicular to the optical axis are fixed.

It is noted that in the variable magnification optical system according to the Sixth Example, in the wide angle end state, the vibration reduction coefficient is 1.54, and the focal length is 72.10 (mm), so that the moving amount of the B group G4B for correcting a rotational camera shake of 0.30 degrees is 0.25 (mm). In the telephoto end state, the vibration reduction coefficient is 2.42, and the focal length is 292.00 (mm), so that the moving amount of the B group G4B for correcting a rotational camera shake of 0.20 degrees is 0.42 (mm).

Table 6 below shows various values of the variable magnification optical system according to the Sixth Example.

TABLE 6 Sixth Example [Surface Data] Surface number r d nd νd Object Plane ∞  1 94.0000 5.600 1.51680 63.88  2 −475.5757 0.200  3 128.0000 1.700 1.62004 36.40  4 39.6000 8.000 1.51680 63.88  5 425.5305 variable  6 −190.0000 1.300 1.69680 55.52  7 20.4656 4.300 1.84666 23.80  8 66.5049 2.063  9 −61.8359 1.200 1.85026 32.35 10 109.1965 variable 11 128.7113 3.300 1.58913 61.22 12 −63.7222 variable 13 37.0000 5.400 1.49700 81.73 14 −45.9212 1.300 1.85026 32.35 15 148.3744 0.200 16 45.1050 3.600 1.48749 70.31 17 −172.8812 4.000 18 (Stop S) ∞ 26.764  19 −95.3704 3.900 1.74950 35.25 20 −14.2257 1.000 1.69680 55.52 21 24.1570 2.279 22 26.2427 4.000 1.62004 36.40 23 −55.0000 2.250 24 −20.2886 1.000 1.84666 23.80 25 −34.0000 BF Image Plane ∞ [Various Data] Variable magnification ratio 4.05 W M T f 72.1 100.0 292.0 FNO 4.69 4.66 6.54 2ω 22.56 16.04 5.50 Ymax 14.25 14.25 14.25 TL 169.32 189.24 221.32 BF 38.93 38.52 65.93 Infinitely distant d5 2.500 25.118 52.806 d10 33.481 28.557 2.155 d12 11.047 13.692 17.068 Close distance d5 2.500 25.118 52.806 d10 34.454 29.917 3.849 d12 10.075 12.332 15.373 [Lens Group Data] Group Starting Surface f 1 1 130.472 2 6 −32.352 3 11 72.809 4 13 142.608 [Values for Conditional Expression] (1) fA/(−fB) = 2.479 (1A) f1/(−fc) = 4.033 (1B) f1fw/ff = 6.295 (2) f1/ff = 1.792 (3) ff/fi = 0.511 (4) fi/(−fB) = 4.779 (5) νFP = 61.22 (6) ff/ft = 0.249

FIGS. 22A, 22B and 22C are graphs showing various aberrations of the variable magnification optical system according to the Sixth Example upon focusing on an infinitely distant object, in which FIG. 22A is in a wide angle end state, FIG. 22B is in an intermediate focal length state, and FIG. 22C is in a telephoto end state.

FIG. 23A is a graph showing meridional transverse aberration of the variable magnification optical system according to the Sixth Example upon focusing on an infinitely distant object in the wide angle end state with carrying out vibration reduction against a rotational camera shake of 0.30 degrees, and FIG. 23B is a graph showing meridional transverse aberration of the variable magnification optical system according to the Sixth Example upon focusing on an infinitely distant object in the telephoto end state with carrying out vibration reduction against a rotational camera shake of 0.20 degrees.

FIGS. 24A, 24B and 24C are graphs showing various aberrations of the variable magnification optical system according to the Sixth Example upon focusing on a close distance object, in which FIG. 24A is in the wide angle end state, FIG. 24B is in the intermediate focal length state, and FIG. 24C is in the telephoto end state.

As is apparent from the respective aberration graphs, the variable magnification optical system according to the Sixth Example shows superb imaging performance as a result of good corrections to various aberrations in the wide angle end state to the telephoto end state, and also shows superb imaging performance upon carrying out vibration reduction and upon focusing on a close distance object.

Seventh Example

FIG. 25 is a sectional view of a variable magnification optical system according to a Seventh Example.

The variable magnification optical system according to the Seventh Example is composed of, in order from an object side, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, and a rear group GR having positive refractive power. The rear group GR is composed of, in order from the object side, a third lens group G3 having positive refractive power, and a fourth lens group G4 having positive refractive power.

The first lens group G1 consists of, in order from the object side, a double convex positive lens L11, and a cemented positive lens constructed by a negative meniscus lens L12 having a convex surface facing the object side cemented with a positive meniscus lens L13 having a convex surface facing the object side.

The second lens group G2 consists of, in order from the object side, a cemented negative lens constructed by a double concave negative lens L21 cemented with a positive meniscus lens L22 having a convex surface facing the object side, and a double concave negative lens L23.

The third lens group G3 consists of a double convex positive lens L31.

The fourth lens group G4 is composed of, in order from the object side, an A group G4A having positive refractive power, a B group G4B having negative refractive power, and a C group G4C having positive refractive power. Meanwhile, an aperture stop S is disposed between the A group G4A and the B group G4B.

The A group G4A consists of, in order from the object side, a cemented positive lens constructed by a double convex positive lens L41 cemented with a double concave negative lens L42, and a double convex positive lens L43.

The B group G4B consists of, in order from the object side, a cemented negative lens constructed by a positive meniscus lens L44 having a concave surface facing the object side cemented with a double concave negative lens L45.

The C group G4C consists of, in order from the object side, a double convex positive lens L46, and a negative meniscus lens L47 having a concave surface facing the object side.

In the variable magnification optical system according to the Seventh Example, the first to fourth lens groups G1 to G4 are moved along the optical axis so that, upon varying magnification between the wide angle end state and the telephoto end state, a distance between the first lens group G1 and the second lens group G2, a distance between the second lens group G2 and the third lens group G3 and a distance between the third lens group G3 and the fourth lens group G4 are varied.

In the variable magnification optical system according to the Seventh Example, the third lens group G3 is moved toward an image side along the optical axis, as the focusing lens group, thereby focusing from an infinitely distant object to a close distance object.

In the variable magnification optical system according to the Seventh Example, the B group G4B is moved, as a vibration reduction group, to have a component in a direction perpendicular to the optical axis, thereby conducting vibration reduction. Meanwhile, upon carrying out vibration reduction, positions of the A group G4A and the C group G4C in a direction perpendicular to the optical axis are fixed.

It is noted that in the variable magnification optical system according to the Seventh Example, in the wide angle end state, the vibration reduction coefficient is 1.61, and the focal length is 72.10 (mm), so that the moving amount of the B group G4B for correcting a rotational camera shake of 0.30 degrees is 0.23 (mm). In the telephoto end state, the vibration reduction coefficient is 2.42, and the focal length is 292.00 (mm), so that the moving amount of the B group G4B for correcting a rotational camera shake of 0.20 degrees is 0.42 (mm).

Table 7 below shows various values of the variable magnification optical system according to the Seventh Example.

TABLE 7 Seventh Example [Surface Data] Surface number r d nd νd Object Plane ∞  1 94.0000 5.600 1.51680 63.88  2 −477.1369 0.200  3 127.9954 1.700 1.62004 36.40  4 39.7182 8.000 1.51680 63.88  5 477.0326 variable  6 −133.8008 1.300 1.69680 55.52  7 20.5210 4.000 1.84666 23.80  8 68.1000 2.028  9 −63.5000 1.200 1.85026 32.35 10 113.2367 variable 11 102.3130 3.400 1.58913 61.22 12 −69.1650 13 39.2000 5.500 1.49700 81.73 14 −39.2000 1.300 1.85026 32.35 15 209.5771 0.200 16 50.7811 3.700 1.48749 70.31 17 −101.5494 1.393 18 (Stop S) ∞ 22.905  19 −80.0000 3.300 1.80100 34.92 20 −18.0344 1.000 1.70000 48.11 21 29.8801 2.000 22 34.2607 3.800 1.60342 38.03 23 −54.3498 7.014 24 −20.2978 1.000 1.77250 49.62 25 −34.3298 BF Image plane ∞ [Various Data] Variable magnification ratio 4.05 W M T f 72.1 100.0 292.0 FNO 4.71 4.68 6.51 2ω 22.58 16.04 5.50 Ymax 14.25 14.25 14.25 TL 169.32 188.35 221.32 BF 42.82 42.30 69.82 Infinitely distant d5 2.500 25.131 52.658 d10 32.209 27.505 2.151 d12 11.251 12.875 16.152 Close distance d5 2.500 25.131 52.658 d10 33.116 28.781 3.756 d12 10.345 11.599 14.546 [Lens Group Data] Group Starting Surface f 1 1 128.381 2 6 −31.506 3 11 70.567 4 13 143.423 [Values for Conditional Expression] (1) fA/(−fB) = 2.044 (1A) f1/(−fc) = 4.075 (1B) f1fw/ff = 6.330 (2) f1/ff = 1.819 (3) ff/fi = 0.492 (4) fi/(−fB) = 4.048 (5) νFP = 61.22 (6) ff/ft = 0.242

FIGS. 26A, 26B and 26C are graphs showing various aberrations of the variable magnification optical system according to the Seventh Example upon focusing on an infinitely distant object, in which FIG. 26A is in a wide angle end state, FIG. 26B is in an intermediate focal length state, and FIG. 26C is in a telephoto end state.

FIG. 27A is a graph showing meridional transverse aberration of the variable magnification optical system according to the Seventh Example upon focusing on an infinitely distant object in the wide angle end state with carrying out vibration reduction against a rotational camera shake of 0.30 degrees, and FIG. 27B is a graph showing meridional transverse aberration of the variable magnification optical system according to the Seventh Example upon focusing on an infinitely distant object in the telephoto end state with carrying out vibration reduction against a rotational camera shake of 0.20 degrees.

FIGS. 28A, 28B and 28C are graphs showing various aberrations of the variable magnification optical system according to the Seventh Example upon focusing on a close distance object, in which FIG. 28A is in the wide angle end state, FIG. 28B is in the intermediate focal length state, and FIG. 28C is in the telephoto end state.

As is apparent from the respective aberration graphs, the variable magnification optical system according to the Seventh Example shows superb imaging performance as a result of good corrections to various aberrations in the wide angle end state to the telephoto end state, and also shows superb imaging performance upon carrying out vibration reduction and upon focusing on a close distance object.

Eighth Example

FIG. 29 is a sectional view of a variable magnification optical system according to an Eighth Example.

The variable magnification optical system according to the Eighth Example is composed of, in order from an object side, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, and a rear group GR having positive refractive power. The rear group GR is composed of, in order from the object side, a third lens group G3 having positive refractive power, a fourth lens group G4 having positive refractive power, and a fifth lens group G5 having negative refractive power.

The first lens group G1 consists of, in order from the object side, a double convex positive lens L11, and a cemented positive lens constructed by a negative meniscus lens L12 having a convex surface facing the object side cemented with a positive meniscus lens L13 having a convex surface facing the object side.

The second lens group G2 consists of, in order from the object side, a cemented negative lens constructed by a double concave negative lens L21 cemented with a positive meniscus lens L22 having a convex surface facing the object side, and a double concave negative lens L23.

The third lens group G3 consists of a double convex positive lens L31.

The fourth lens group G4 is composed of, in order from the object side, an A group G4A having positive refractive power, a B group G4B having negative refractive power, and a C group G4C having positive refractive power. Meanwhile, an aperture stop S is disposed between the A group G4A and the B group G4B.

The A group G4A consists of, in order from the object side, a cemented positive lens constructed by a double convex positive lens L41 cemented with a double concave negative lens L42, and a double convex positive lens L43.

The B group G4B consists of, in order from the object side, a cemented negative lens constructed by a positive meniscus lens L44 having a concave surface facing the object side cemented with a double concave negative lens L45.

The C group G4C consists of a double convex positive lens L46.

The fifth lens group G5 consists of a negative meniscus lens L51 having a concave surface facing the object side.

In the variable magnification optical system according to the Eighth Example, the first to the fifth lens groups G1 to G5 are moved along the optical axis so that, upon varying magnification between the wide angle end state and the telephoto end state, a distance between the first lens group G1 and the second lens group G2, a distance between the second lens group G2 and the third lens group G3, a distance between the third lens group G3 and the fourth lens group G4 and a distance between the fourth lens group G4 and the fifth lens group G5 are varied.

In the variable magnification optical system according to the Eighth Example, the third lens group G3 is moved toward an image side along the optical axis, as the focusing lens group, thereby focusing from an infinitely distant object to a close distance object.

In the variable magnification optical system according to the Eighth Example, the B group G4B is moved, as a vibration reduction group, to have a component in a direction perpendicular to the optical axis, thereby conducting vibration reduction. Meanwhile, upon carrying out vibration reduction, positions of the A group G4A and the C group G4C in a direction perpendicular to the optical axis are fixed.

It is noted that in the variable magnification optical system according to the Eighth Example, in the wide angle end state, the vibration reduction coefficient is 1.62, and the focal length is 72.10 (mm), so that the moving amount of the B group G4B for correcting a rotational camera shake of 0.30 degrees is 0.23 (mm). In the telephoto end state, the vibration reduction coefficient is 2.42, and the focal length is 292.00 (mm), so that the moving amount of the B group G4B for correcting a rotational camera shake of 0.20 degrees is 0.42 (mm).

Table 8 below shows various values of the variable magnification optical system according to the Eighth Example.

TABLE 8 Eighth Example [Surface Data] Surface number r d nd νd Object Plane ∞  1 94.0000 5.600 1.51680 63.88  2 −475.1178 0.200  3 128.0000 1.700 1.62004 36.40  4 39.6000 8.000 1.51680 63.88  5 485.7465 variable  6 −132.5210 1.300 1.69680 55.52  7 20.5172 4.000 1.84666 23.80  8 68.1000 2.042  9 −63.5000 1.200 1.85026 32.35 10 115.6235 variable 11 101.8918 3.400 1.58913 61.22 12 −69.9544 variable 13 39.2000 5.500 1.49700 81.73 14 −39.2000 1.300 1.85026 32.35 15 212.6596 0.200 16 51.4164 3.700 1.48749 70.31 17 −99.0728 1.373 18 (Stop S) ∞ 23.152  19 −80.0000 3.300 1.80100 34.92 20 −17.8244 1.000 1.70000 48.11 21 29.4302 2.000 22 34.1234 3.800 1.60342 38.03 23 −54.6969 variable 24 −20.3466 1.000 1.77250 49.62 25 −34.1069 BF Image Plane ∞ [Various Data] Variable magnification ratio 4.05 W M T f 72.1 100.0 292.0 FNO 4.71 4.69 6.49 2ω 22.58 16.06 5.50 Ymax 14.25 14.25 14.25 TL 169.32 188.16 221.32 BF 43.07 42.89 70.02 Infinitely distant d5 2.500 24.944 52.518 d10 32.517 27.845 2.150 d12 10.875 12.288 16.347 d23 6.586 6.430 6.515 Close distance d5 2.500 24.944 52.518 d10 33.434 29.131 3.779 d12 9.958 11.001 14.718 d23 6.586 6.430 6.515 [Lens Group Data] Group Starting Surface f 1 1 128.138 2 6 −31.607 3 11 70.925 4 13 71.734 5 24 −67.420 [Values for Conditional Expression] (1) fA/(−fB) = 2.058 (1A) f1/(−fc) = 4.054 (1B) f1fw/ff = 6.215 (2) f1/ff = 1.807 (3) ff/fi = 0.989 (4) fi/(−fB) = 2.046 (5) νFP = 61.22 (6) ff/ft = 0.243

FIGS. 30A, 30B and 30C are graphs showing various aberrations of the variable magnification optical system according to the Eighth Example upon focusing on an infinitely distant object, in which FIG. 30A is in a wide angle end state, FIG. 30B is in an intermediate focal length state, and FIG. 30C is in a telephoto end state.

FIG. 31A is a graph showing meridional transverse aberration of the variable magnification optical system according to the Eighth Example upon focusing on an infinitely distant object in the wide angle end state with carrying out vibration reduction against a rotational camera shake of 0.30 degrees, and FIG. 31B is a graph showing meridional transverse aberration of the variable magnification optical system according to the Eighth Example upon focusing on an infinitely distant object in the telephoto end state with carrying out vibration reduction against a rotational camera shake of 0.20 degrees.

FIGS. 32A, 32B and 32C are graphs showing various aberrations of the variable magnification optical system according to the Eighth Example upon focusing on a close distance object, in which FIG. 32A is in the wide angle end state, FIG. 32B is in the intermediate focal length state, and FIG. 32C is in the telephoto end state.

As is apparent from the respective aberration graphs, the variable magnification optical system according to the Eighth Example shows superb imaging performance as a result of good corrections to various aberrations in the wide angle end state to the telephoto end state, and also shows superb imaging performance upon carrying out vibration reduction and upon focusing on a close distance object.

According to the above-mentioned examples, it is possible to realize a variable magnification optical system which can superbly suppress variations in various aberrations upon varying magnification from the wide angle end state to the telephoto end state and variations in various aberrations upon focusing from an infinitely distant object to a close distance object and can downsize a focusing group and make it light in weight. That is, in this variable magnification optical system, by downsizing the focusing group and making it light in weight, the focusing group can be driven by a small-sized motor or mechanical mechanism, thereby realizing a high speed and silent focusing operation with avoiding enlargement of a lens barrel.

Note that each of the above described Examples is a concrete example of the invention of the present application, and the invention of the present application is not limited to them. The contents described below can be properly adopted without deteriorating optical performance of the variable magnification optical systems according to the embodiment of the present application.

Although the variable magnification optical systems each having a four or five group configuration are illustrated above as examples of the variable magnification optical systems according to the embodiment of the present application, the present application is not limited to them and the variable magnification optical systems having other configurations, such as a six group configuration and the like, can be configured. Concretely, a configuration that a lens or a lens group is added to a most object side or a most image side of the variable magnification optical system according to each of the above-mentioned examples is also possible.

Further, in each of the above-mentioned examples, the second lens group is illustrated as an intermediate group disposed at an image side of the first lens group and having negative refractive power, but the present invention is not limited to such configuration. Further, in each of the above-mentioned examples, the third lens group is illustrated as a focusing group disposed at an image side of the second lens group as an intermediate group and having positive refractive power, but the present invention is not limited to such configuration. Further, in each of the above-mentioned examples, the fourth lens group is illustrated as an image side group disposed at an image side of the focusing group and having positive refractive power, but the present invention is not limited to such configuration. Concretely, it is also possible that a lens group having a positive or negative refractive power is disposed between the first lens group and the intermediate group (the second lens group) and distances between these lens groups are varied upon varying magnification. Further, it is also possible that a lens group having a positive or negative refractive power is disposed between the intermediate group (the second lens group) and the focusing group (the third lens group) and distances between these lens groups are varied upon varying magnification. Further, it is also possible that a lens group having a positive or negative refractive power is disposed between the focusing group (the third lens group) and the image side group (the fourth lens group) and distances between these lens groups are varied upon varying magnification.

In the variable magnification optical system according to each of the above-mentioned examples, it is preferable that the vibration reduction group is disposed at an image side of the focusing group, and it is more preferable that other lens(es) is(are) disposed between the focusing group and the vibration reduction group. Further, regarding the rear group, in a case where other lens(es) is(are) disposed between the focusing group and the vibration reduction group, it is preferable that an air distance between a lens facing an object side of the vibration reduction group and the vibration reduction group is the largest one of the air distances in the rear group.

Further, regarding the rear group, it is preferable that an aperture stop is disposed between the focusing group and the vibration reduction group, and it is more preferable that an aperture stop is disposed at a position facing an object side of the vibration reduction group. Meanwhile, the function of an aperture stop may be substituted by a lens frame without disposing a member as the aperture stop.

Further, the refractive power of the C group is positive in each of the Examples, but it may be negative.

Further, a sub-combination of feature groups of respective examples also is deemed as an invention of the present application.

Further, in the variable magnification optical system according to each of the above-mentioned examples, the whole third lens group is used as a focusing group, but a part of lens group or two or more lens groups may be used as a focusing group. Further, it is preferable that the focusing group has a positive refractive power. Further, one or two lens components are enough for configuration of the focusing group, but more preferably the focusing group is composed of one lens component. The focusing group can be used for auto focus, and also can be suitably driven by a motor for auto focus, for example, an ultrasonic motor, a stepping motor, a VCM motor or the like.

Further, in the variable magnification optical system according to each of the above-mentioned examples, any lens group in the entirety thereof or a portion thereof can be shifted in a direction including a component perpendicular to the optical axis as a vibration reduction group, or rotationally moved (swayed) in an in-plane direction including the optical axis for conducting vibration reduction. Particularly, in the variable magnification optical system according to each of the above-mentioned examples, it is preferable that the B group is used as a vibration reduction group. Further, although vibration reduction group may be composed of one cemented lens as in each of the above-mentioned examples, it may be also composed of a single lens or two or more lens components without particularly limiting the number of lenses. Further, it is preferable that the vibration reduction group has negative refraction power. Further, it is preferable that the vibration reduction group is composed of a part of one lens group, and it is more preferable that one lens group is divided into three parts and the vibration reduction group is composed of a center part of the three parts. Furthermore, it is preferable that one lens group is divided into three positive-negative-positive parts or positive-negative-negative parts, and the vibration reduction group is composed of a center negative part of the three parts.

Further, in the variable magnification optical system according to each of the above-mentioned examples, a lens surface of a lens may be a spherical surface, a plane surface, or an aspherical surface. Further, each lens may be formed by a glass material, a resin material or a composite of a glass material and a resin material. When a lens surface is a spherical surface or a plane surface, lens processing and assembly adjustment become easy, so that deterioration in optical performance caused by a lens processing error and an assembly adjustment error can be prevented and thus it is preferable. Moreover, even if the image plane is shifted, deterioration in optical performance is little conveniently. When a lens surface is an aspherical surface, the aspherical surface may be fabricated by a grinding process, a glass molding process that a glass material is formed into an aspherical shape by a mold, or a compound type process that a resin material on a glass surface is formed into an aspherical shape. Further, a lens surface may be a diffractive optical surface, and a lens may be a graded-index type lens (GRIN lens) or a plastic lens.

Moreover, lens surfaces of lenses configuring the variable magnification optical system according to each example may be coated with anti-reflection coating. With this contrivance, it is feasible to reduce a flare as well as ghost and attain high contrast and high optical performance. Particularly, in the variable magnification optical system according to each of the above-mentioned examples, it is preferable to coat an object side lens surface of the second lens counted from a most object side with anti-reflection coating.

Next, a camera equipped with a variable magnification optical system according to an embodiment of the present application, will be explained with referring to FIG. 33.

FIG. 33 is a sectional view showing a configuration of the camera equipped with the variable magnification optical system according to the embodiment of the present application.

As shown in FIG. 33, a camera 1 is a so-called mirrorless camera of lens-replaceable type equipped with the variable magnification optical system according to the above-mentioned First Example as an imaging lens 2.

In the present camera 1, light emitted from an unillustrated object is converged by the imaging lens 2, and an object image is formed on an imaging surface of an imaging unit 3 through an unillustrated OLPF (Optical low pass filter). Then, the object image is photo-electrically converted by a photoelectric conversion element in the imaging unit 3 to generate an image of the object. This image is displayed on an EVF (Electronic view finder) 4 mounted in the camera 1. Accordingly, a photographer can observe the object image through the EVF 4.

Further, when the photographer presses an unillustrated release button down, the image of the object generated in the imaging unit 3 is stored in an unillustrated memory. In this manner, the photographer can take a picture of an object by the present camera 1.

Hence, the variable magnification optical system according to the above First Example, mounted as the imaging lens 2 in the present camera 1, has excellent optical performance and a focusing lens group reduced in weight. That is, the present camera 1 can realize excellent optical performance and high speed focusing operation. Moreover, even when a camera is configured to mount thereon the variable magnification optical system according to each of the above Second to Eighth Examples, as the imaging lens 2, the camera can provide the same advantageous effects as the above camera 1 can do. Further, even when the variable magnification optical system according to each of the above examples is mounted on a camera of single-lens reflex type having a quick return mirror and observing an object by a finder optical system, the camera can provide the same advantageous effects as the above camera 1 can do.

Finally, an outline of a method for manufacturing a variable magnification optical system according to the present embodiment, is described with referring to FIG. 34.

FIG. 34 is a flowchart showing an outline of a method for manufacturing the variable magnification optical system according to the present embodiment.

A method for manufacturing a variable magnification optical system according to the present embodiment as shown in FIG. 34 comprises a step S1 of preparing a first lens group disposed at a most object side and having positive refractive power, an intermediate group disposed at an image side of the first lens group and having negative refractive power, a focusing group disposed at an image side of the intermediate group and having positive refractive power, the focusing group being moved upon focusing, and an image side group disposed at an image side of the focusing group and having positive refractive power, and a step S2 of arranging the first lens group, the intermediate group, the focusing group, and the image side group such that, upon varying magnification, a distance between the first lens group and the intermediate group, a distance between the intermediate group and the focusing group and a distance between the focusing group and the image side group are varied, the image side group being composed of, in order from an object side, an A group having positive refractive power, a B group satisfying the following conditional expression (1) with respect to the A group and having negative refractive power, and a C group: 1.67<fA/(−fB)<2.80  (1)

where fA denotes a focal length of the A group, and fB denotes a focal length of the B group.

According to the method for manufacturing a variable magnification optical system of the present embodiment, it is possible to manufacture a variable magnification optical system having excellent optical performance and a focusing lens group reduced in weight in order to attain high speed focusing operation. 

What is claimed is:
 1. A variable magnification optical system, comprising: a first lens group disposed at a most object side and having positive refractive power; an intermediate group disposed at an image side of the first lens group and having negative refractive power; a focusing group disposed at an image side of the intermediate group and having positive refractive power, the focusing group being moved upon focusing; and an image side group disposed at an image side of the focusing group and having positive refractive power; upon varying magnification, a distance between the first lens group and the intermediate group, a distance between the intermediate group and the focusing group and a distance between the focusing group and the image side group being varied; the image side group comprising, in order from an object side, an A group having positive refractive power, a B group satisfying the following conditional expression with respect to the A group and having negative refractive power, and a C group: 1.67<fA/(−fB)<2.80 where fA denotes a focal length of the A group, and fB denotes a focal length of the B group; and the following conditional expression being satisfied: 2.50<f1/(−fc)≤4.365 where f1 denotes a focal length of the first lens group, and fc denotes a focal length of the intermediate group.
 2. A variable magnification optical system according to claim 1, wherein the following conditional expression is satisfied: 0.25<ff/fi<1.10 where ff denotes a focal length of the focusing group, and fi denotes a focal length of the image side group.
 3. A variable magnification optical system according to claim 1, wherein the following conditional expression is satisfied: 1.80<fi/(−fB)<5.20 where fi denotes a focal length of the image side group.
 4. A variable magnification optical system according to claim 1, wherein the focusing group comprises at least one positive lens and the following conditional expression is satisfied: 58.00<νFP where νFP denotes an Abbe number for d-line (wavelength 587.6 nm) of the positive lens.
 5. A variable magnification optical system, comprising: a first lens group disposed at a most object side and having positive refractive power; an intermediate group disposed at an image side of the first lens group and having negative refractive power; a focusing group disposed at an image side of the intermediate group and having positive refractive power, the focusing group being moved upon focusing; and an image side group disposed at an image side of the focusing group and having positive refractive power; upon varying magnification, a distance between the first lens group and the intermediate group, a distance between the intermediate group and the focusing group and a distance between the focusing group and the image side group being varied; the image side group comprising, in order from an object side, an A group having positive refractive power, a B group satisfying the following conditional expression with respect to the A group and having negative refractive power, and a C group: 1.67<fA/(−fB)<2.80 where fA denotes a focal length of the A group, and fB denotes a focal length of the B group; and the following conditional expression being satisfied: 0.492≤ff/fi<1.10 where ff denotes a focal length of the focusing group, and fi denotes a focal length of the image side group.
 6. A variable magnification optical system according to claim 5, wherein the following conditional expression is satisfied: 2.50<f1/(−fc)<6.20 where f1 denotes a focal length of the first lens group, and fc denotes a focal length of the intermediate group.
 7. A variable magnification optical system according to claim 5, wherein the following conditional expression is satisfied: 1.80<fi/(−fB)<5.20.
 8. A variable magnification optical system according to claim 5, wherein the focusing group comprises at least one positive lens and the following conditional expression is satisfied: 58.00<νFP where νFP denotes an Abbe number for d-line (wavelength 587.6 nm) of the positive lens.
 9. A variable magnification optical system, comprising: a first lens group disposed at a most object side and having positive refractive power; an intermediate group disposed at an image side of the first lens group and having negative refractive power; a focusing group disposed at an image side of the intermediate group and having positive refractive power, the focusing group being moved upon focusing; and an image side group disposed at an image side of the focusing group and having positive refractive power; upon varying magnification, a distance between the first lens group and the intermediate group, a distance between the intermediate group and the focusing group and a distance between the focusing group and the image side group being varied; and the image side group comprising, in order from an object side, an A group having positive refractive power, a B group satisfying the following conditional expression with respect to the A group and having negative refractive power, and a C group: 1.67<fA/(−fB)≤1.836 where fA denotes a focal length of the A group, and fB denotes a focal length of the B group.
 10. A variable magnification optical system according to claim 9, wherein the following conditional expression is satisfied: 2.50<f1/(−fc)<6.20 where f1 denotes a focal length of the first lens group, and fc denotes a focal length of the intermediate group.
 11. A variable magnification optical system according to claim 9, wherein the following conditional expression is satisfied: 0.25<ff/fi<1.10 where ff denotes a focal length of the focusing group, and fi denotes a focal length of the image side group.
 12. A variable magnification optical system according to claim 9, wherein the following conditional expression is satisfied: 1.80<fi/(−fB)<5.20 where fi denotes a focal length of the image side group.
 13. A variable magnification optical system according to claim 9, wherein the focusing group comprises at least one positive lens and the following conditional expression is satisfied: 58.00<νFP where νFP denotes an Abbe number for d-line (wavelength 587.6 nm) of the positive lens.
 14. A method for manufacturing a variable magnification optical system, comprising steps of: arranging a first lens group disposed at a most object side and having positive refractive power, an intermediate group disposed at an image side of the first lens group and having negative refractive power, a focusing group disposed at an image side of the intermediate group and having positive refractive power, the focusing group being moved upon focusing, and an image side group disposed at an image side of the focusing group and having positive refractive power; the arrangement being such that, upon varying magnification, a distance between the first lens group and the intermediate group, a distance between the intermediate group and the focusing group and a distance between the focusing group and the image side group are varied; and the method further comprising at least one or more of the following features (A), (B) and (C): (A) configuring the image side group to comprise, in order from an object side, an A group having positive refractive power, a B group satisfying the following conditional expression with respect to the A group and having negative refractive power, and a C group: 1.67<fA/(−fB)<2.80 where fA denotes a focal length of the A group, and fB denotes a focal length of the B group, and satisfying the following conditional expression: 2.50<f1/(−fc)≤4.365 where f1 denotes a focal length of the first lens group, and fc denotes a focal length of the intermediate group; (B) configuring the image side group to comprise, in order from an object side, an A group having positive refractive power, a B group satisfying the following conditional expression with respect to the A group and having negative refractive power, and a C group: 1.67<fA/(−fB)<2.80 where fA denotes a focal length of the A group, and fB denotes a focal length of the B group, and satisfying the following conditional expression: 0.492≤ff/fi<1.10 where ff denotes a focal length of the focusing group, and fi denotes a focal length of the image side group; (C) configuring the image side group to comprise, in order from an object side, an A group having positive refractive power, a B group satisfying the following conditional expression with respect to the A group and having negative refractive power, and a C group: 1.67<fA/(−fB)≤1.836 where fA denotes a focal length of the A group, and fB denotes a focal length of the B group. 